This invention relates in general to frame assemblies for vehicles. More specifically, this invention relates to an improved method for manufacturing a vehicle frame assembly including a pair of side rails, each of which is formed from a single closed structural member that formed by hydroforming so as to having a plurality of mounting areas integrally formed thereon.
Many land vehicles in common use, such as automobiles, vans, and trucks, include a frame assembly that is supported upon a plurality of ground-engaging wheels by a resilient suspension system. The structures of known frame assemblies can be divided into two general categories, namely, separate and unitized. In a typical separate frame assembly, the structural components of the body portion and the frame portion are separate and independent from one another. When assembled, the frame portion of the assembly is resiliently supported upon the vehicle wheels by the suspension system and serves as a platform upon which the body portion of the assembly and other components of the vehicle can be mounted. Separate frame assemblies of this general type are found in most older vehicles, but remain in common use today for many relatively large or specialized use modern vehicles, such as large vans, sport utility vehicles, and trucks. In a typical unitized body and frame assembly, the structural components of the body portion and the frame portion are combined into an integral unit that is resiliently supported upon the vehicle wheels by the suspension system. Unitized body and frame assemblies of this general type are found in many relatively small modem vehicles, such as automobiles and minivans.
One well known example of a separate type of vehicular frame assembly is commonly referred to as a ladder frame assembly. A ladder frame assembly includes a pair of longitudinally extending side rails that are joined together by a plurality of transversely extending cross members. The cross members connect the two side rails together and provide desirable lateral, vertical, and torsional stiffness to the ladder frame assembly. The cross members can also be used to provide support for various components of the vehicle. Depending upon the overall length of the vehicle and other factors, the side rails of a conventional ladder frame assembly may be formed either from a single, relatively long structural member or from a plurality of individual, relatively short structural members that are secured together. For example, in vehicles having a relatively short overall length, it is known to form each of the side rails from a single integral structural member that extends the entire length of the vehicle frame assembly. In vehicles having a relatively long overall length, it is known to form each of the side rails from two or more individual structural members that are secured together, such as by welding, riveting, or bolting to provide a unitary structural member that extends the entire length of the vehicle frame assembly.
Traditionally, the side rails of known vehicle frame assemblies have been formed exclusively from open structural members, i.e., structural members that have a non-continuous cross sectional shape (U-shaped or C-shaped members, for example). Thus, it is known to use a single integral open structural member to form a side rail that extends the entire length of the vehicle frame assembly, as described above. Additionally, it is known to secure a plurality of such open structural members together to form the individual sections of a unitary side rail for a vehicle frame assembly, as also described above. However, the use of open structural members to form the side rails for vehicle frame assemblies has been found to be somewhat inefficient for several reasons from a manufacturing standpoint. First, it is relatively time consuming and expensive to bend multiple portions of the side rails to conform to a desired final shape, as is commonly necessary. Second, after such bending has been performed, a relatively large number of brackets or other mounting devices must usually be secured to each of the side rails to facilitate the attachment of the various components of the vehicle to the frame assembly. Third, in those instances where the side rails are formed from a plurality of individual sections, it has been found difficult to maintain dimensional stability throughout the length of the side rail when the individual side rail sections are secured together. Thus, known vehicle frame assemblies having side rails formed from one or mote open structural members have been found to be somewhat inefficient to manufacture.
More recently, it has been proposed to form the side rails in vehicle frame assemblies from closed structural members, i.e., structural members that have a continuous cross sectional shape (tubular or box-shaped members, for example). Thus, it is known to use a single integral closed structural member to form a side rail that extends the entire length of the vehicle frame assembly, as described above. Additionally, it is known to secure one a plurality of such closed structural members together to form the individual sections of a unitary side rail for a vehicle frame assembly, as also described above. Furthermore, it is known to secure a combination open and closed structural members together to form the individual sections of a unitary side rail for a vehicle frame assembly.
In vehicle frame assemblies formed from closed structural members, it is known that hydroforming may be used to deform the closed structural member into a desired shape. Hydroforming is a well known process that uses pressurized fluid to deform a closed structural member into a desired shape. To accomplish this, the structural member is initially disposed between two die sections of a hydroforming apparatus which, when closed together, define a die cavity having a desired final shape. Thereafter, the structural member is filled with a pressurized fluid, typically a relatively incompressible liquid such as water. The pressure of the fluid is increased to a magnitude where the structural member is expanded outwardly into conformance with the die cavity. As a result, the structural member is deformed into the desired final shape.
Hydroforming has been found to be a desirable process for deforming the closed structural member because the individual side rail section can be quickly and easily deformed to have a desired cross sectional shape. For example, the individual side rail section may be formed having a generally rectangular or box-shaped cross section. This cross sectional shape is advantageous not only because it provides strength and rigidity to the individual side rail section, but also because it provides vertically and horizontally oriented side surfaces which facilitate the attachment of various brackets and mounts used to support other components of the vehicle on the vehicle frame structure. However, even in known hydroformed side rail structures, the attachment of these various brackets and mounts is a relatively expensive and time consuming process. Thus, it would be desirable to provide an improved method for manufacturing a side rail for use in a vehicle frame assembly that eliminate the need for attaching these various brackets and mounts.
This invention relates to an improved method for manufacturing a vehicle frame assembly including a pair of side rails, each of which is formed from a single closed structural member that is formed by hydroforming so as to having a plurality of mounting areas integrally formed thereon. The frame assembly includes a pair of longitudinally extending side rails having a plurality of transverse cross members extending therebetween. Each of the side rails is formed from a single integral closed structural member that extends the entire length of the frame assembly. The cross members extend generally perpendicular to the side rails and may be formed having any conventional structure. Each of the side rails is manufactured having a plurality of integrally formed mounting structures to facilitate the connection of the various components (not shown) of the vehicle directly to the frame assembly without the use of any brackets and mounts. The side rails are hydroformed to desired shapes and have respective pluralities of apertures and protrusions formed therein. The side rails are formed into desired shapes such that the apertures and protrusions can be located in exactly the same positions relative to the frame assembly as the corresponding apertures and protrusions provided on the various brackets and mounts of the prior art frame assembly. As a result, the other components of the vehicle can be connected directly to the side rails to form the frame assembly. This direct side rail mounting structure eliminates the need for the various brackets and mounts provided in the prior art frame assembly and, as a result, greatly reduces the time and expense involved in manufacturing the ladder frame assembly of this invention.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.